Spectral measurements of wide-bandwidth radio frequency (RF) signals have traditionally been performed using a swept spectrum analyzer, which provides scalar analysis (amplitude only, no phase information) of the signal of interest. To provide for demodulation analysis of complex digitally-modulated RF waveforms, vector (amplitude and phase) spectral measurements must be made on the signal. For example, two common methods of performing vector spectral measurements of RF signals are Digital Oscilloscope (DO) and Wide-Bandwidth Spectrum Analyzer (WBSA).
DO utilizes a high-speed digital oscilloscope to digitize a wide RF spectrum, including the signal of interest. However, DO has limited amplitude resolution (effective digitizer bits), is subject to Nyquist sampling images, and is a relatively expensive instrument. WBSA is a spectrum analyzer with wide intermediate frequency (IF) circuitry, such that a high-speed IF digitizer can be used to measure a wide-bandwidth RF signal. In comparison, a Narrow Bandwidth Spectrum Analyzer (NBSA), for of discussion, is a spectrum analyzer with an IF digitizer bandwidth less than the bandwidth of the signal of interest. The disadvantages of a WBSA include having a bandwidth limited to several hundred megahertz (MHz) and mixing images due to bypassing of its preselector. A WBSA is also a relatively expensive instrument.
In the case of non-repetitive RF waveforms, these two conventional methods are valid methods to obtain vector spectral measurements. However, in the special case of repetitive waveforms, a more accurate and efficient approach is needed.